1. Field of the Invention
The present invention relates to a radio communication device that converts reflected high-frequency signal power from an antenna into a direct current power and uses the converted electric power, and also to an electric power supplying method for the radio communication devices.
2. Description of the Related Art
In a transmitter of a portable radio communication terminal, matching circuits are designed to make impedance matching between a high-frequency power amplifier and an antenna in order to radiate power, which is outputted from the high-frequency power amplifier, efficiently from the antenna. However, because the impedance of the antenna changes depending on the way of holding by a user or a usage environment, power reflection from the antenna occurs.
As countermeasures to this problem, there exists a method of providing a controllable matching circuit between the high-frequency power amplifier and the antenna to make a reflected wave smaller (Patent literature 1), a method of canceling the reflected wave by a part of transmitting electric power (Patent literature 2), a method of canceling the reflected wave by using the reflected wave (Patent literature 3) and so on.    Patent literature 1: Japanese Patent Application Laid-open No. 2000-295055    Patent literature 2: Japanese Patent Application Laid-open No. H02-151130    Patent literature 3: Japanese Patent Application Laid-open No. H09-116459
Since a matching circuit with an impedance tuning function is added to the output side of the power amplifier in the method of Patent literature 1, a loss is given to a transmission signal. So, it is necessary to use a power amplifier capable of greater power amplification in order to transmit signals at a desired electric power, and it has a drawback of reducing efficiency. In the method of Patent literature 2, a part of the transmission power is used to cancel the reflected wave, so that efficiency deteriorates by that amount. In the method of Patent literature 3, an electric power for amplifying a part of the reflected wave is necessary, and the electric power efficiency of the entire portable radio communication device worsens.